The invention relates to a method of transmitting messages between bus users which are each connected with a communication bus for exchanging messages, and having a diagnostic device for a disturbance of the communication bus.
The necessity of mutually connecting several bus users, such as control units and sensors, increasingly exists in modern vehicles. Such control units are, for example, an electronic engine control and the control of an automatic transmission. In order to read out faults for such a control unit during a repair shop stay, it is known from German Published Patent Application DE 39 34 974 A1 to arrange a diagnostic bus as a diagnostic device in the vehicle. One bus line is used for the transmission of control signals and the other line is provided as a status line. This results in considerable constructive expenditures just for the diagnosis.
From German Patent Document DE 19837242 C, a method of the above-mentioned type is known, in the case of which a data transmission also takes place by way of a separate diagnostic bus in the event of a fault. The diagnostic bus represents a redundant data bus. As in German Patent Document DE 39 34 974 A1,considerable constructive expenditures are also required here. Furthermore, a possibly occurring fault, as a rule, cannot be seen in the data transmission because the diagnostic bus will then automatically “intervene”. If, as in the case of German Patent Document DE 39 34 974 A1,the status of the transmitted message is checked, the status does not change in the event of a fault.
It is an object of the invention to provide a method of transmitting messages between bus users of a vehicle, which permits a reliable diagnosis of a disturbance in the data transmission, specifically in the case of a data transmission between two bus users, without any special expenditures.
This object is achieved by a method of transmitting messages between bus users which are each connected with a communication bus for exchanging messages, and having a diagnostic device for a disturbance of the communication bus, wherein in a diagnostic operating mode differing from the normal operation, for the diagnosis of a message transmission between two bus users, the bus user receiving the message is asked by the diagnostic device to output the message on the communication bus. Advantageous further developments of the invention are described and claimed herein.
In an operating mode which differs from the normal operation, using the diagnostic device, the bus user normally receiving the message can be caused, in a targeted manner, to output the message to the communication bus. If the bus user does not do so, or if the message is damaged, a disturbance is present. However, it can then not yet be determined where the disturbance is situated.
For localizing the source of the disturbance, a third bus user not participating in this message transmission in the normal operation, can be caused in the diagnostic operation to receive this message. The status of this message for the three bus users is subsequently read out. If the fault is present in the sender, the two receiving bus users have the same status (“no message present”). If the fault is in the receiver, the two receivers have different statuses.
The method according to the invention is particularly suitable for a bilateral message transmission. For messages which are transmitted in the normal operation between more than two bus users, in the operating mode differing from the normal operation, the addition of another bus user is no longer required. Here, it is sufficient for the status of this message to be read out for all bus users participating in this message transmission. A fault of the sender does not change the message status of the receivers. A fault in a receiver can be recognized by the different status of this receiver in comparison to the other receivers.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.